The first full sequencing of a coral genome has revealed that corals originated much earlier than previously thought, and at least one important species is far more fragile than environmentalists had feared. Today, scientists from Japan's Okinawa Institute of Science and Technology announced that they've sequenced the genome of Acropora digitifera[2], a spindly reef-building coral that populates much of the Indo-Pacific oceans. Researchers identified 23,688 protein-coding genes. Comparing the coral's genome with its cnidarian relatives—jellyfish, sea anemones, and hydras—they found that corals emerged some 500 million years ago, which is 250 million years earlier than their earliest known fossil records. The researchers also discovered that A. digitifera lacks the enzymes necessary to produce an essential amino acid, cysteine. That means the coral likely relies on microscopic symbiotic organisms called dinoflagellates to biosynthesize cysteine for it, making the coral particularly susceptible to changing climate conditions that endanger its tiny helpers.